No one saw it coming. The earliest signs were from Cape Race, Newfoundland, just about the easternmost point on the continent—the very definition of the end of the road. It’s not the sort of place that usually makes news: When the Titanic sank, Cape Race got the distress signal, but that was back in 1912. It’s been pretty quiet ever since.

In November, though, people started noticing a bizarre number of snowy owls there. One or two would be normal, but 18, as reported on Nov. 22? “It is now officially a BIG Snowy Owl event,” Newfoundland birding blogger Bruce Mactavish wrote excitedly. “How big will it get? . . . In extreme Snowy Owl years I think the Cape Race road record is more than 30. . . . [this] may be just a hint of what is about to happen.”

The next day there were 42 owls there.

About a week later the count was 138. And on December 8 Mactavish tallied 206 of the ghostly raptors. Owls flushed from the roadside as he drove out the cape, or crowded together, three or four at a time on each little hillock, in gusty snow squalls and rising wind. “Anywhere you looked you could see them flying low over the barrens,” he reported that night to the local birding list. From one spot, he said, he counted 75 with a single sweep of his binoculars.

Across the map—from Minnesota to the Maritimes, all around the Great Lakes and down the Atlantic Coast to the Carolinas—snowy owls were appearing like magic. One even showed up in Bermuda, another in Florida (just the third in recorded history). They were flooding across the border in numbers that hadn’t been seen in perhaps half a century.

This record-breaking irruption—as such unpredictable invasions of northern birds are known—was unfolding just as scientists are making one stunning discovery after another about these gorgeous and charismatic birds, turning much of what we thought we knew about snowy owls on its head.

We now know that these birds are among the world’s great avian nomads, ranging thousands of miles across the Arctic. They somehow ferret out areas with exploding populations of lemmings, a favorite summer food, provisioning their nests with literal heaps of dead rodents. Well fed and fertile, the female owls produce chicks in astonishing numbers—youngsters that, when conditions are right, move south en masse.

Every four years or so there’s a modest irruption, timed to four-year lemming cycles. But when the stars align perfectly—superabundant food, a high concentration of nesting owls, early and deep snows in the north—there can be a huge invasion like the one this year.

Still, even when all the conditions are right, it can be tough to predict an avalanche. In fact, scientists like Jean-François Therrien, working in the Canadian Arctic, have found that at least some snowy owls will actually go north for the winter, spending months of endless darkness amid the desolation of the polar ice pack, a behavior no one suspected until recently.

Snowy owls, frankly, are largely a mystery—which is why this winter’s invasion provided an unparalleled opportunity. Through several hectic weeks in December, some colleagues and I assembled dozens of collaborators across the irruption zone, each bringing their own specialty to bear in a frenzied effort that we have named Project SNOWstorm. (SNOW is the shorthand, four-letter code that banders and birders use for this bird.)

Some of us are trapping and tagging owls to track their movements; others are testing blood samples to determine a bird’s sex and genetic makeup, or analyzing tiny snippets of feathers whose chemical isotopes may shed light on just where the owls originated. Some are coordinating wildlife veterinarians and rehabilitators to gather data from injured and ill owls, enlisting wildlife pathologists to conduct necropsies on dead ones, and taking tissue samples that could be tested for toxins and contaminants.

I thought I was going to have a quiet winter, finishing up a book on owls, until the news spilled down from Newfoundland. “We won’t live long enough to see something like this again,” my friend Dave Brinker said, shaking his head when I told him about the count.

It was a week before Christmas when i joined brinker in his white Maryland Department of Natural Resources truck on the beach at Assateague Island National Seashore, on the Eastern Shore, watching an ivory bird that glowed in the morning sun. The owl was snugged down along an old, wave-smoothed telephone pole lying on the sand. It was lightly flecked with black spots and bars, and occasionally it would turn its head and sleepily blink its yellow eyes at us. Otherwise it utterly ignored us and the occasional surf fisherman who drove by below the high-tide line, not far away.

Crouched beneath the cap in the back of the truck were Therrien, who is a scientist at Hawk Mountain Sanctuary in Pennsylvania, and raptor biologist Michael Lanzone, a golden eagle expert whose company, Cellular Tracking Technologies, makes bird-tracking devices. Lanzone held the trigger line for a spring-loaded bownet set in the sand a hundred feet behind the truck, in the middle of which a leather-jacketed pigeon sat alluringly.

At least we hoped it was alluring. If all went as planned, we’d catch the owl and suit it up with a new style of cutting-edge GPS transmitter Lanzone has designed. This next-generation tracking system logs incredibly precise locations in three dimensions (latitude, longitude, and altitude), using the GPS satellite system that guides both military missiles and your car. Then it dials up the ever-expanding cellular network to basically phone home once a day with all the data.

The snowy made a few halfhearted passes over the trap. Conventional wisdom holds that these birds, chased south by hunger, far from familiar surroundings and tasty lemmings, wander until they perish from starvation. But we are learning that privation isn’t what drives them south; it’s plenty. This owl behaved not like a famished predator but more like a sated diner turning up his nose at an unappetizing morsel. After each pass, it returned to its drowsy vigil in the dunes, paying us no mind.

For all we knew, this owl might have hatched from one of the nests that Therrien studied last summer in Canada, where there were some early signs that an extraordinary snowy owl invasion was in the making.

“We had to move from our long-term study area on Bylot Island [in the Canadian territory of Nunavut] because there were no lemmings, and no snowy owls,” he told us while we waited. The rodents boom and bust in great cycles, so a place like Bylot may swarm with lemmings one year but be devoid of them the next. Research shows snowy owls have an uncanny ability to find lemmings, as they did on the tundra of northern Quebec, a thousand miles north of Montreal near Hudson Strait. After a tip from Inuit communities in the area, Therrien and his colleagues arrived to find a hotbed of lemmings and nesting owls.

“Lemmings were everywhere,” he said. Snowy owls were nesting in dense pockets, almost like small colonies; it’s likely that owls from across the Canadian Arctic had converged in that region to profit from the lemming peak. The owls’ success was off the charts, Therrien said. Instead of fledging just one to three chicks, as is normal, each nest was pumping out six, seven, or eight fat babies, full to bursting with as many lemmings as the chicks could eat. One of his colleagues took a picture that sums up the fecundity of the tundra. It shows an owl nest with four unhatched eggs (probably with more on the way) surrounded by 70 dead lemmings and eight dead voles brought in by the overly enthusiastic male.

Lemmings are the engine that propels an irruption, but snowy owls are anything but fussy eaters—a fact that Norman Smith, a SNOWstorm collaborator who directs the Blue Hills Trailside Museum in Milton, Massachusetts, knows well.

Smith has been studying snowy owls since 1981, largely at Boston’s Logan Airport, and he’s dismissive of claims that the snowies that come south are doomed to starve. “Will some of them die when they come here? Absolutely. Some may even starve to death, but that’s true of any young raptor,” he said. “But the data that we’ve collected show that in years when you have lots of snowy owls, the birds are actually in better condition. They’re in good body weight, they have lots of fat. These birds are moving because it was a banner year for lemmings, and there are just more owls to travel farther south.”

Smith’s job catching owls at the airport requires following a strict protocol. He must drive his truck onto a mirrored platform so airport security staff can check the undercarriage for bombs. Then he heads out to the tarmac and taxiways, where this winter he’s seen as many as 18 snowies at a time. A snowy owl is a danger to a jet, and the reverse is even truer—by Christmas five owls had already been killed by plane strikes.

So Smith fishes for owls in the noisy dusk of the airport, dropping a baited bownet a few hundred feet from a perched snowy as darkness comes on, his headlights conveniently illuminating the lure, and a cut-off fishing rod poking out his truck window with the trigger line stretched taut. A pounce, a sharp pull, and he’s moving the owl to safer haunts 20 or 30 miles down the coast, a trip he’d already made more than 50 times by Christmas.

Over the years he’s learned just how competent and fearless a hunter the snowy owl really is. Snowies will tackle almost anything with fur or feathers, from rats to feral cats to skunks and muskrats and birds—especially birds. “They’re a real fast-flying owl, able to pursue something like black ducks or mergansers,” he told me earlier this winter in his rapid-fire Boston accent. “Or like American kestrels. You’ll have a kestrel hovering out there and—boom!—the owl plucks it right out of the air. I’ve seen them take great blue herons, Canada geese, brant. Even snow buntings, which are incredibly agile birds, but the owls actually catch them in the air, in flight.”

As with so many areas of wildlife research, new tracking methods are opening windows on snowy owl ecology. For example, Therrien and his team in Canada have found that their satellite-tagged adults show amazing variability in where they go for the winter. Some head south, into North Dakota or Newfoundland; one was killed this winter by a car in Minnesota. Others stay in the high Arctic. The distances they move have been astounding—one traveled more than 2,000 miles to its wintering grounds.

In 2011 Therrien’s team published a study showing evidence that a number of their tagged owls were actually going farther north in the winter, up to the Hudson and even Davis straits, spending the season on what appeared to be empty, godforsaken pack ice. When they first saw the satellite tracks, the Canadian team assumed it had to be a mistake. “We were like, ‘Oh, God, did we do something wrong? Are we sure we know what we’re doing with the map?’ ” Therrien said. “But [the owls] did that for three consecutive winters, and we realized, well, we’ve got a story here.”

They were right. When the scientists compared their owls’ locations with high-resolution satellite photographs, they realized the birds were concentrating along open-water leads, known as polynyas, in the endless darkness of the Arctic winter. Although no one has braved the almost unbearable conditions to see for themselves, it appears the owls are hunting hardy sea ducks like eiders wintering in these open spots—a rare case of a terrestrial predator switching to a marine environment for part of the year.

Come summer, instead of returning to their former breeding sites, the tagged owls continue to ricochet all over the Arctic, settling an average of 450 miles from where they had nested the previous summer. Only one owl tagged on Bylot Island returned there to nest. That’s almost unheard of among birds. Most species, from hummingbirds to eagles, practice what is known as site fidelity—they return to the same places each year to breed and to spend the winter. After all, that’s the safest course: If you’ve successfully nested or wintered someplace once, chances are you can do so again. Moving somewhere unknown is risky. But in summer and winter, snowy owls appear to be consummate itinerants, constantly prowling around the rooftop of the world. Because their summer food supply, lemmings, is so explosive and ephemeral, returning to a previous breeding location may be a guarantee of failure, not success.

Why, if snowy owls are capable of wintering in the highest latitudes of the Arctic, did so many come south this winter? Therrien isn’t sure, but the birds he and his colleagues have been tracking were all adults, and the vast majority of the irruptive birds that came south in 2013 were juveniles. It could be that the more seasoned adults try to stay farther north, closer to the breeding grounds. “Adults are, by definition, more experienced hunters, whereas young birds are not,” he said. “It might take more skill to catch a duck than a mouse, but who knows? We believe adults would occupy the areas closer to the breeding grounds, including sea ice, leaving other birds to look for options down south. But all this remains hypothesis because we don’t have data.”

We’ve learned to expect the unexpected with snowy owls, which is why I can’t predict what we’ll learn from the owls we’re following this winter. No one has ever studied their wintering behavior this closely; this is terra incognita.

As the sun sank behind the Assateague Island dunes, the owl we were trying to catch finally roused from its slumber. Its head bobbed back and forth as it stared at the lure, and it lifted its tail to squirt a stream of excreta onto the sand. It launched itself, swooped low over the net—and kept on going.

We scrambled to scoop up the gear and raced down the beach, frantically scanning for the owl in the gathering dusk. We found it perched on a high dune and reset the trap. This time as soon as it saw the pigeon it raced toward us, making several false approaches before dropping on the lure. Within moments, Lanzone sprung the net and hoisted the big, pale bird in his hands.

Gently spreading its five-foot wings, we could see this was a young bird, with even-aged flight feathers showing no signs of molt. The inner wing feathers were spotted, not barred—the mark of a male. Brinker took measurements while Lanzone positioned the transmitter on the owl’s back.

By now it was dark. A nearly full moon shining through high clouds cast everything in silver light as we walked the owl out through the loblolly pine forest and into the dunes, the sound of waves crashing in the darkness not far ahead. “Okay, guy, show us what you can do,” Lanzone said to the owl, lofting him into the air. Two flaps of the powerful wings and he was gone, enveloped by the twilight.

Except that he was still very much with us. Once a day his transmitter checked in, showing us how he moved up and down the slender barrier island, then began an unexpected flight north. He spent a day loafing on the tip of Cape Henlopen in Delaware, then at dusk flew out to perch on the Harbor of Refuge lighthouse before winging 38 miles up the length of Delaware Bay.

The bird, which we named Assateague, lingered on an isolated spit along Cohansey Cove, surrounded by empty salt marsh, then moved down the New Jersey bayshore to the hamlet of Reed’s Beach, just north of Cape May, where he settled in for a week.

Every evening I would log on to Lanzone’s website, enter my password, and download the latest data from Assateague’s transmitter—an astoundingly detailed glimpse into the winter life of a snowy owl. The GPS fixes confirmed what birders (who initially kept a close eye on him) were telling us: that during the day, Assateague was just hanging out, roosting on beachfront rooftops, the tip of the jetty, or pilings in Bidwell Creek.

Night was the real revelation. Traditional satellite telemetry, at best, logs a single location every day for the tagged bird. As we tested these transmitters on an owl for the first time, locations were being recorded from Assateague at least every 30 minutes.

At dusk, he became a pelagic hunter, flying out into Delaware Bay, patrolling a mile or two offshore and often perching on channel markers and buoys, presumably scouring the moonlit water for sleeping black ducks and scaup. In the weeks ahead he moved farther and farther up the New Jersey coast, haunting the backwaters and beaches of its barrier islands. At one point he made a midnight stop to take in the sights on the end of Atlantic City’s famous Steel Pier.

At press time, Assateague was in New Jersey’s lower Barnegat Bay, sometimes sunning himself on condo rooftops, sometimes staying for days at a stretch on tiny islands that are, in winter, as close to wilderness as you’ll find on the Atlantic coast.

Assuming he dodges the myriad dangers that threaten any young raptor, much less a naive wanderer from the Arctic, he’ll begin heading home in early spring. By May he and most of his kin will be back in the Far North. Somehow, with luck, and by whatever alchemy their species has used for eons, they will find the current lemming explosion, wherever it may be in the Canadian Arctic. Assateague may still be too young to breed this spring, but other males will court mates, flying in exaggerated undulations with lemmings dangling from their beaks; females will build their nests on windswept hillocks and lay their eggs, keeping them warm against the chill.

And Assateague’s solar-powered transmitter, which should last for years, will keep to its regular task, triangulating his position and storing that information in the unit’s prodigious memory bank. If Assateague comes south again, even years from now, to a place with cell phone coverage—maybe to the Canadian prairies, where so many snowy owls winter each year, or to the Maritimes or even New England—then those data showing all of his wanderings will pour out, a final gift from the historic snowstorm of 2014.

Storm Tracker!

Participants in Project SNOWstorm are volunteering their time and expertise, and the public is playing an equally important role by helping to support the project. A crowd-funding campaign was launched on January 2 with a two-month goal to raise $20,000 for six additional transmitters. Hundreds of people responded, and the project miraculously exceeded its goal in barely two weeks. Several state ornithological groups also chipped in to sponsor transmitters, and additional donations are helping to defray the expense of DNA and blood and feather testing. You can follow Project SNOWstorm, including updates about tagged owls and other aspects of the research, at projectsnowstorm.org.

This story originally ran in the March-April 2014 issue as "Have Lemmings, Will Travel."